DE102011083332A1 - Method for automatically activating or deactivating sailing mode of motor vehicle, involves rolling the vehicle in sailing mode and disabling currently activated sailing mode when the current speed exceeds preset threshold value - Google Patents

Abstract

The vehicle is rolled in sailing mode, and the currently activated sailing mode is disabled (S6), when the current vehicle speed exceeds predetermined threshold value. The threshold value is set as the sum of minimum vehicle speed and the maximum allowable speed increase. Any time during the period of a currently active sailing mode, the minimum vehicle speed is defined as a function of the smallest vehicle speed, while immediately preceding the coherent time interval. The time interval is either the entire duration of straight activated sailing mode or the immediate past period. An independent claim is included for a device for automatically activating or deactivating sailing mode of motor vehicle mounted with internal combustion engine.

Description

The invention relates to a method and an apparatus for automatically activating or deactivating a sailing mode in a motor vehicle with an internal combustion engine in response to driving requirements of a driver of the motor vehicle, as indicated in the preambles of the independent claims.

Such a method and such a device are known from WO 2005/084995 A1 known.

A conventional motor vehicle with internal combustion engine slows down because of the engine drag torque when the driver takes his foot off the accelerator pedal. Only on steep gradients is the engine drag torque insufficient to reduce vehicle speed. This also depends on the vehicle mass, the current vehicle speed and the currently engaged gear.

In motor vehicles with internal combustion engine and automatic transmission, there is a so-called. Sail mode in which the drive train is automatically opened when the driver takes his foot off the accelerator pedal. The internal combustion engine may be idled in sail mode or - e.g. in the case of a start / stop automatic - also completely switched off. In the sail mode, the engine drag torque is eliminated to save fuel.

Various driver interactions such as Propulsion or braking requirements by actuating the drive or brake pedal or also actuating the gear selection lever lead to the closing of the drive train, i. to a termination of the sailing mode, and to a conventional vehicle behavior. With this general logic, the driver has control over enabling or disabling the sail mode, and can choose between sail mode and conventional engine drag torque.

It is to be expected that the drivers adapt their driving style to the presence of the sailing mode. This means that the driver does not expect the vehicle to slow significantly if he takes his foot off the accelerator pedal. However, the vehicle behavior in the sail mode is different when the road on which the vehicle is currently traveling has a slope or occurs along the way. In particular, the vehicle in the sail mode even at a moderate slope, which the driver may not even perceive, faster, while this effect occurs in conventional roles with engine drag torque only at a greater gradient, which perceives the driver usually.

To solve this problem, in the above mentioned WO 2005/084995 A1 It is proposed to automatically deactivate a currently activated sailing mode even if the current vehicle speed exceeds or substantially exceeds a threshold value. This threshold may be a value preset by the driver, or it may be automatically adjusted depending on the current and / or forward grade, with the current or forward grade being determined using satellite navigation.

It is time-consuming, error-prone and not delay-free to determine the current or previous gradient using satellite navigation.

One might consider calculating the vehicle acceleration in the direction of travel either by differentiating the vehicle speed or measuring directly and automatically deactivating a sail mode when the calculated or measured vehicle acceleration exceeds a threshold. However, the differentiation of the vehicle speed results in a noisy acceleration signal, and a directly measured acceleration signal is noisy per se, which is why only relatively large vehicle accelerations could be detected reliably.

The invention is based on the object to provide a simple, fast, accurate and reliable method for setting a speed threshold above which a currently activated sail mode is automatically deactivated.

This object is achieved by a method and by a device having the features of the independent patent claims.

Advantageous developments of the invention are specified in the dependent claims.

According to the invention, the threshold above which a currently activated sail mode is automatically deactivated is set as the sum of a minimum vehicle speed and a maximum permissible speed increase.

The term "minimum vehicle speed" in this case is intended to denote a value which is equal to the current vehicle speed if it remains constant, but less than the current vehicle speed, if the vehicle during the duration of a currently activated Sail mode has become faster, so the vehicle speed was previously smaller.

Preferably, at any time during the duration of a currently activated sailing mode, the minimum vehicle speed is determined as a function of the smallest measured vehicle speed at a contiguous time interval immediately preceding that time, the contiguous time interval being the entire duration of a currently activated sail mode or an immediate may be of the past period.

Specifically, the minimum vehicle speed may be set either as the smallest vehicle speed measured in the contiguous time interval or as a type of average of vehicle speeds measured in the contiguous time interval.

The term "maximum permissible speed increase" in this context denotes a value which should either represent a preset fixed value or be a value dependent on the current vehicle speed, in particular a preset fraction thereof, or one of the two aforementioned values plus one variable, which is proportional to a fixed preset maximum allowable acceleration.

The inventive method can be carried out in particular in a motor vehicle with automatic transmission or automatic clutch, but is not limited thereto. For even in a motor vehicle having a manual (i.e., foot or hand) drive train to open, a sail mode may be mimicked by eliminating the need for propulsion and braking requirements, i. As a rule, a non-actuation of accelerator pedal and brake pedal, the internal combustion engine so much fuel / air mixture is supplied that the engine friction loss is almost compensated. Even in such a case, the inventive method can be applied accordingly. Note that under a "sail mode" in a motor vehicle having a manually-openable powertrain (ie, usually a manual transmission and / or a foot-operated clutch) is understood to mean something other than an automatic cruise control, in which not only the engine friction loss but also all other losses, especially those due to roll and air resistance, are compensated, and also something other than a fuel cut, in which all the engine drag torque is experienced.

The following is a description of embodiments with reference to the drawings. Show:

1 two typical driving situations in which a motor vehicle may experience an unexpected acceleration;

2 the basic principle of activating or deactivating as well as allowing or prohibiting a sailing mode in a motor vehicle so that it does not experience any unexpected acceleration; and

3 a flowchart for explaining a logic for terminating a sailing mode in a motor vehicle so that it does not experience unexpected acceleration.

The driver of a motor vehicle controls the vehicle speed according to the driving situation. The vehicle accelerates when the driver depresses the accelerator pedal, and the vehicle slows down when the driver takes his foot off the accelerator pedal. However, in the case of a steep downhill descent, the vehicle may accelerate without the driver's intention. In such a situation, the driver usually has to brake in order to reduce or keep the vehicle speed constant.

A motor vehicle with automatic transmission and / or automatic clutch that can switch to the so-called. Sail mode automatically opens the clutch when the driver takes his foot off the accelerator pedal. Subsequently, the vehicle acceleration or deceleration essentially depends only on air resistance and rolling friction, as well as the current road gradient, since the engine drag torque is eliminated. In the case of downhill driving, a vehicle accelerates in the sail mode at a lower grade, or accelerates faster than a conventional vehicle when rolling without operating the accelerator and clutch pedals. However, a vehicle acceleration not intended by the driver is not desired and must be prevented.

1 Figure 2 shows two typical driving situations which may lead to unexpected vehicle acceleration, namely situation 1), driving on a constant medium or high grade road, and situation 2), driving on a gradually increasing gradient road. In both situations, there are several reasons why the sail mode may be undesirable to the driver. These include the feeling of insufficient control of the vehicle, too rapid reduction of the distance to a vehicle in front, exceeding a speed limit, the presence of a tight curve ahead or the presence of a gate od. Like. A wall at the end of a ramp, for example, in a Underground parking leads.

In order for the vehicle does not accelerate significantly, the two situations mentioned above require different approaches. In situation 1), the vehicle is normally not initially in the sail mode, and the vehicle may be prevented from entering the sail mode by setting a sail-forbidden flag in the control electronics responsible for the sail mode when vehicle acceleration is expected.

In situation 2), the vehicle may initially be in the sail mode and then begin to get faster due to the increasing gradient. In this case, the sailing mode is terminated by setting a sail-end request in the control electronics, and in addition, the sailing-prohibited flag can be set. This principle is in 2 shown.

A prediction of whether the vehicle will accelerate in situation 1) could be based on the strength of the road gradient. This can be measured or estimated by monitoring the vehicle behavior independently of the sail mode. If the strength of the road gradient is above a certain threshold, sailing is to be prevented. This threshold may be a constant value or a speed dependent value, and it may be combined with a certain dwell time.

In many cases, such as e.g. in situation 2), the road gradient changes during sailing. It may be that the vehicle does not accelerate at the beginning of a sailing phase, but only later, when the road gradient is stronger. For these cases, it is sufficient to stop sailing based on one of the following three methods: First, the road grade can be determined and compared with a threshold, second, the vehicle acceleration can be determined and compared to a threshold, and third, the vehicle speed change during sailing are compared to a threshold. This can happen regardless of whether the Sail Forbidden flag is set based on the grade itself. However, the cause for the termination may also be a set sail-forbidden flag, so that sailing is not possible as long as the sail-forbidden flag is not cleared. The strategy for clearing the sailing-prohibited flag depends on the respective control strategy and may be different for each cause. For example, the sail-forbidden flag is cleared only when the driver depresses the accelerator pedal after the sail mode has been terminated by exceeding the allowed acceleration. Alternatively, the sail-forbidden flag is automatically cleared when the cause no longer exists (eg, the road grade is below a threshold). This allows the sail mode to be restarted without driver interaction.

The first method, terminating the sail mode based on the road grade, is known per se and has several disadvantages: it takes some time to reliably detect the road grade, and during that time the vehicle may be accelerating too much. In addition, small gradients, which nonetheless can lead to acceleration, are difficult to measure because weak signals would have to be extracted from strong, noisy signals.

For the second method, ending the sailing mode based on the vehicle acceleration, the vehicle acceleration may either be calculated from the vehicle speed or directly measured as the vehicle longitudinal acceleration. In both cases, however, one can not use relatively small thresholds because differentiating the speed signal gives a noisy acceleration signal and because a direct acceleration measurement per se is noisy. z. For example, the average acceleration is 0.139 m / s ² when the vehicle speed increases by 5 km / h in 10 seconds.

In the third method according to the invention, terminating the sailing mode based on a speed increase during sailing, the acceleration itself is not limited, but the effect of the acceleration is controlled and limited. The advantage of this method is that the effect of acceleration is directly controlled and no differentiation is necessary. The use of the vehicle speed signal allows for small thresholds (eg, vehicle speed increases of 5 km / h).

The basic algorithm of such vehicle speed control is shown in the flowchart of FIG 3 shown.

When the sailing mode is started (step 1), a threshold Vmax for the vehicle speed in the sailing mode is set as the current, ie, current vehicle speed V plus a fixed preset maximum speed increase ΔV (step S2). It may be that the current vehicle speed V becomes smaller during the sailing mode. Therefore, the threshold Vmax is continuously adjusted to the current vehicle speed V by being set as the smaller of the two values V + ΔV and the previous Vmax (step S3). In step S4, it is checked whether the current vehicle speed V is greater than the threshold value Vmax. If the result in step S4 is No, is checked in step S5, whether the sail mode is still active or by some other condition, eg. As a driver interaction has been disabled. If the result in step S5 is "Yes", it returns to step S3. If the result in step S4 is Yes, the sailing mode is deactivated (step S6), and the algorithm is ended (step S7). If the result in step S5 is No, the algorithm is also terminated (step S7).

If the enabling or disabling of the sailing mode also includes allowing the sailing mode to be prohibited by means of a sailing-forbidden flag, as in connection with 2 is explained, the sail-forbidden flag is set in step S6, so that the vehicle does not re-enter the sailing mode. The sailing-forbidden flag may be cleared by driver interaction, eg when the driver depresses the accelerator pedal, or automatically without driver interaction when e.g. B. the speed is below a threshold set for it.

The above means that an activated sail mode is deactivated when the current vehicle speed exceeds a threshold set as the sum of a minimum vehicle speed and a maximum allowable speed increase, the minimum vehicle speed being the minimum vehicle speed measured during the sail mode ,

The basic algorithm described above does not allow a constant small acceleration during sailing. However, this is desirable in sailing situations where the driver wants to use the grade for light acceleration. In this regard, the above vehicle speed control algorithm can be improved by adding, in the minimum choice in step S3, a value Vmax which is the product of a preset allowable acceleration a and a suitably selected sampling time T: Vmax = min (V + ΔV, Vmax + a · T)

In a further development, the maximum permissible speed increase .DELTA.V is not a fixed value, but speed-dependent by z. B. is 10% of the current vehicle speed, so that at higher vehicle speeds, higher speed increases are allowed without the sail mode is disabled.

In summary, the algorithm described causes, during a sailing phase, the minimum, d. H. smallest vehicle speed is determined and only a limited exceeding of this speed is allowed without the sailing phase is terminated.

In a refinement thereof, the minimum vehicle speed can be tracked slowly to the current vehicle speed. This can be done by filtering a vehicle speed signal, i. H. a kind of averaging, in which also younger signal components can be weighted more strongly. The sailing phase is only ended when the filtered minimum vehicle speed is exceeded by a certain amount. This allows for slow speed increases without ending the sailing phase. For larger, possibly surprising for the driver speed increases, however, the sailing phase is terminated.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005/084995 A1 [0002, 0007]

Claims (9)

A method for automatically enabling or disabling a sail mode in a motor vehicle with an internal combustion engine in response to propulsion or braking requirements of a driver of the motor vehicle, wherein the motor vehicle in the sail mode rolls substantially unpowered, with a just activated sail mode disabled if the current vehicle speed exceeds a threshold, characterized in that the threshold is set as the sum of a minimum vehicle speed and a maximum allowable speed increase. A method according to claim 1, characterized in that at any time during the duration of a currently activated sailing mode, the minimum vehicle speed is determined as a function of the minimum vehicle speed measured in a contiguous time interval immediately preceding that time. A method according to claim 1 or 2, characterized in that the contiguous time interval is either the entire duration of a currently activated sailing mode or an immediately preceding period thereof. Method according to one of the preceding claims, characterized in that the minimum vehicle speed either As the smallest vehicle speed measured in the continuous time interval, or As a kind of mean value of vehicle speeds measured in the contiguous time interval. Method according to one of the preceding claims, characterized in that the maximum allowable speed increase either - is a preset fixed value or Is a value dependent on the current vehicle speed, in particular a pre-set fraction thereof, or - One of the two aforementioned values plus a size that is proportional to a preset maximum allowable acceleration. Method according to one of the preceding claims, characterized in that the method is carried out in a motor vehicle with automatic transmission and / or automatic clutch. Method according to one of the preceding claims, characterized in that the method is carried out in a motor vehicle with a manually openable powertrain by the sailing mode is mimicked in the absence of propulsion and braking requirements, that supplied to the engine so much fuel / air mixture will almost completely compensate engine friction loss, especially at rather low engine speeds. Method according to one of the preceding claims, characterized in that the method is carried out on a downward slope. Device for automatically activating or deactivating a sailing mode in a motor vehicle with an internal combustion engine in response to driving or braking requirements of a driver of the motor vehicle, wherein the motor vehicle in the sailing mode rolls substantially without propulsion, characterized in that the device for performing the method according to any one of the preceding claims is formed.

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